An electrolysis cell uses electricity to convert water to hydrogen and oxygen in gas phase.
Known electrolysis cells consist of either: a liquid alkaline electrolyser which utilizes a porous membrane between the electrodes to separate the hydrogen and oxygen gases or a polymer electrolyte electrolyser which utilizes a proton exchange membrane in order to separate the hydrogen and oxygen gases produced through the electrolysis process. The electrolysis cell further includes an anode positioned along a first face of the proton exchange membrane and a cathode positioned along a second opposite face of the proton exchange membrane.
Known membranes in liquid alkaline electrolysers are generally made from porous plastics whilst in polymer electrode electrolysers the known proton exchange membranes are semi-permeable membranes generally made from ionomers and designed to conduct protons while being impermeable to gases, such as oxygen and hydrogen. Proton exchange membranes can be made from either pure polymer membranes or from composite membranes where other materials are embedded in a polymer matrix.
A first disadvantage of all types of membranes is the current flow restriction brought about it.
A further disadvantage brought about by the membranes is the increase in distance between the electrodes which results in increased resistance A further disadvantage of the known Liquid Alkaline Membranes is the decrease of efficiency with an increase in current density. The efficiency of the known proton exchange membranes goes down as the voltage applied across the cell goes up, due to poor gas removal from the membrane. Also, the electrodes cannot be stacked too close together, as this will inhibit gas removal.
A further disadvantage of the known Liquid Alkaline Membranes is its inability to function effectively under high temperatures and high pressure.
A further disadvantage of the known proton exchange membrane is the high cost of the membrane, since it requires that a noble-metal catalyst (typically platinum) be used to separate the hydrogen's electrons and protons. The platinum catalyst is also extremely sensitive to carbon monoxide poisoning, making it necessary to employ an additional reactor to reduce carbon monoxide in the fuel gas if the hydrogen is derived from an alcohol or hydrocarbon fuel. This again adds to the cost of using the known proton exchange membrane.
Further disadvantages of the know proton exchange membranes are their poor conductivity at lower relative humidity and their poor mechanical properties at temperatures above approximately 100° C. The operating temperature of these membranes is relatively low and temperatures near 100° C. are not high enough to perform useful cogeneration.
Prior art document PCT/IB2011/053050 in the name of HYDROX HOLDINGS LIMITED entitled “Method and apparatus for producing gas”, describes the use of a liquid alkaline electrolyser employing a hydrodynamic barrier instead of a porous or proton exchange membrane to achieve electrolysis. This invention results in a huge improvement in terms of manufacturing and operating costs and size.
In this specification, the term “combustible fluid” includes within its scope combustible gas containing predominantly hydrogen and/or oxygen in gas phase.